1. Field of the Invention
The present invention relates to an electronic component module, and more specifically, to an electronic component module that is provided with a ceramic substrate. In particular, the present invention relates to a high-frequency module that includes a number of terminal electrodes arranged on the rear surface.
2. Description of the Related Art
A high-frequency module is an example of an electronic component module that is provided with a ceramic substrate. A high-frequency module that integrates devices having various functions, such as switches, filters, couplers, baluns and amplifiers, is used for wireless devices, such as mobile communication devices and wireless LANs. The high-frequency module is configured so that surface mounting components, such as semiconductor devices and ceramic capacitors, which define functional devices, are mounted on the front surface of a ceramic multilayer substrate, wherein wiring that electrically interconnects surface mounting components and functional devices, such as capacitors and inductors, are embedded in the ceramic multilayer substrate. An example of such a high-frequency module is shown in FIG. 12. The high-frequency module 27 is mounted on a printed wiring board 20 as a motherboard in a wireless device. A number of terminal electrodes 28 are provided on the rear surface 27a of the high-frequency module 27. The high-frequency module 27 is mounted on the printed wiring board 20, and the terminal electrodes 28 on the side of the high-frequency module 27 and the surface electrodes 20 on the side of the printed wiring board 20 are welded together using solder 22. The terminal electrodes 28, which are also called “lands”, have been arranged to completely surround the rear surface 27a of the high-frequency module 27 along the outer periphery, including the corner portions. This arrangement is not only applied to high-frequency modules but also to other electronic components that are provided with ceramic substrates.
FIG. 13 shows, in the case of the high-frequency module 27, a state in which a motherboard on which the electronic component module is mounted is subjected to a shock due to a drop, or other external force. When bending or deformation is developed in the printed wiring board 20 as a motherboard, stress concentration occurs at soldered portions between the terminal electrodes 28 on the side of the high-frequency module 27 as an electronic component module and the electrodes on the motherboard side. As a result, the ceramic substrate 2 included in the electronic component module can easily develop a crack 29 or peeling of the terminal electrodes 28 may occur. However, in recent years there has been a need for wireless devices, such as mobile communication devices, that have high durability and reliability against a shock such as that due to a drop. For this reason, electronic component modules must to have enhanced resistance against a shock such as that due to a drop (hereinafter, called “shock resistance”).
In order to improve shock resistance, Japanese Unexamined Patent Application Publication No. 2003-218489 (Patent Document 1) discloses a structure in which recesses or openings are provided in terminal electrodes that are arranged at the four corners of a rear surface. Japanese Unexamined Patent Application Publication No. 2003-179175 (Patent Document 2) discloses a structure in which circular arc-shaped cutouts are provided in terminal electrodes that are arranged at the four corners. Japanese Unexamined Patent Application Publication No. 2003-338585 (Patent Document 3) discloses a structure in which the outer shapes of terminal electrodes that are arranged at the four corners are wave-shaped. These inventions consider that, when the wireless device is subjected to an impact, terminal electrodes that are arranged at the four corners are subjected to a large impact force. Thus, the inventions are intended to enhance the bonding strength between the terminal electrodes at the four corners and at solder portions.
However, there is a definite limit to how much the bonding strength can be improved only by changing the shapes of terminal electrodes as disclosed in the Patent Documents 1 to 3. In other words, there has been a definite limit to how much the shock resistance can be improved using techniques in the known art that are directed to enhancing the bonding strength of the terminal electrodes at the four corners where stress tends to be concentrated.